The present invention relates to a brake fluid pressure retaining unit for retaining brake fluid pressure within a wheel cylinder after a driver releases a brake pedal.
A brake fluid pressure retaining unit is disclosed in Japanese Laid-open Patent Publication No.60-12360. In this brake fluid pressure retaining unit when a brake pedal is released, brake fluid pressure is retained within a wheel cylinder until a starting operation is initiated and driving force is exerted on a vehicle such as by depressing an accelerator pedal in the case of an automatic transmission vehicle or by releasing a clutch pedal and depressing an accelerator pedal in the case of a manual transmission vehicle. This eliminates unintentional backward movement or displacement of the vehicle and hence facilitates the starting operation of the vehicle on a slope.
When starting off a motor vehicle on a down slope, the driver often releases the brake pedal instead of exerting driving force on the vehicle such that the vehicle starts to move due to its own weight. However if the vehicle is equipped with the above brake fluid pressure retaining unit, the vehicle could not start on the slope after releasing the brake pedal since the brake fluid pressure keeps on acting within the wheel cylinder until the starting operation is initiated. The brake fluid pressure retaining unit works irrespective of the inclination of the slope. In order to eliminate this drawback, Japanese Laid-open Patent Publication No. 63-43854 discloses a brake fluid pressure retaining unit, in which an inclination detecting means for detecting up slope or down slope and a switch which is turned on when the back gear of the transmission is selected are provided such that the brake fluid pressure retaining unit merely actuates when the vehicle climbs the slope in a forward or rearward direction.
The present invention seeks to provide a novel brake fluid pressure retaining unit, which can eliminate the aforementioned drawback without requiring the detection of up or down slope.
According to the present invention, there is provided a brake fluid pressure retaining unit for retaining brake fluid pressure within a wheel cylinder after releasing a brake pedal, the brake fluid pressure retaining unit comprising:
a brake fluid pressure reduction speed control means for retaining reduction speed of the brake fluid pressure within the wheel cylinder less than that of brake pedal load applied by a driver.
With such brake fluid pressure retaining unit when the brake pedal load applied by the driver is released, the brake fluid pressure within a wheel cylinder does not immediately decrease to zero as is in the normal run. The brake fluid pressure is retained within the wheel cylinder until the starting operation of the vehicle is initiated. In other words, the brake fluid pressure continues to act within the wheel cylinder during the time required for a pedal-changing action from the brake pedal to the accelerator pedal. This facilitates a smooth start of the vehicle on an up slope since the vehicle is prevented from unintentional backward displacement.
On a down slope, however, since the reduction speed of the brake fluid pressure within the wheel cylinder is slow, when releasing the brake pedal, the brake fluid pressure within the wheel cylinder gradually decreases to such an extent that the vehicle can start to move due to its own weight. Although it takes time, the brake fluid pressure in the end decreases to the amount corresponding to the brake pedal load applied by the driver after loosening the brake pedal BK. Therefore, the driver can start off the vehicle on the down slope merely by releasing or loosening the brake pedal BK and without operating the accelerator pedal.
According to the present invention, the brake fluid pressure reduction speed control means of the aforementioned brake fluid pressure retaining unit is formed by a restriction in a brake fluid pressure channel (brake fluid pressure circuit) arranged between a master cylinder at which the brake fluid pressure is generated in accordance with a brake pedal load applied by the driver and the wheel cylinder.
In such construction, when the brake pedal load is reduced, the brake fluid within the wheel cylinder returns to the master cylinder through the restriction in the brake fluid pressure channel between the master cylinder and the wheel cylinder. Since a flow of the brake fluid is restricted at the restriction, reduction speed of the brake fluid within the wheel cylinder will be less than that of the brake pedal load applied by the driver.
The present invention also seeks to provide a brake fluid pressure retaining unit for retaining brake fluid pressure within a wheel cylinder after releasing a brake pedal, wherein said brake fluid pressure retaining unit retains reduction speed of the brake fluid pressure within the wheel cylinder less than that of brake pedal load applied by a driver.